ART: Fix RegTypeCache::FromUnresolvedMerge().

Do not assume that the BitVector memory is zero-initialized.

Also fix reg_type_test memory leaks reported by valgrind by
constructing ArenaStack and ScopedArenaAllocator in each
individual test.

Bug: 27500678
Change-Id: Ic6b2b6ebeab2c5c6e993a0232c5d4a0159aabea3
2 files changed